The mechanisms of osteoclast recruitment, differentiation, and action at the bone surface are poorly understood. Recent observations support the hypothesis that bone resorbing osteoclasts are of vascular origin. In addition many osteoclast responses to humoral and microenvironmental cues are in all likelihood mediated by cell surface components. The proposed studies are intended to test the hypothesis that specific osteoclast cell surface markers play a role in osteoclast differentiation and regulation. In conjunction with this approach we intend to study interactions between bone cells, bone cell precursor populations and extracellular matrices during osteoclast cytodifferentiation. Such studies will contribute to our understanding of normal and inflammatory bone loss and aid in devising therapies for arthritic, diabetic, and periodontal disease associated osteopenia. We propose to accomplish the objectives outlined in this application by utilizing an osteoclast isolation procedure that results in osteoclast populations enriched 80-90% and quantities of cells up to 30 million. A cell culture system has also been described in which circulating monocytes transform into multinucleated giant cells. These cell systems in addition to marrow cells and osteoblast culture systems will be utilized coordinately with osteoclast specific monoclonal antibodies to identify factors involved in osteoclastogenesis. Specific osteoclast surface components will be analyzed for their functional roles by monoclonal antibody blocking techniques. These antigens will be further characterized biochemically. Immunohistochemical and Immunocytochemical analysis as well as quantitative Radioimmunoassay (RIA) and Enzyme-Linked Immunoassay (ELISA) will be utilized to follow the emergence of osteoclast specific phenotypic markers. The goal of this proposal is to begin to gain insight into cell surface changes associated with osteoclast development and function that may regulate normal and pathological bone loss. Moreover a better understanding of how the bone microenvironment influences osteoclast development and action should be obtained from these studies.